Snap action
Snap action is a term from vehicle technology . A snap shift is a shift over more than one stage (e.g. from 4th to 2nd) in automatic transmissions .
Due to the design, "classic" automatic transmissions ( multi- plate clutch actuated torque converters with planetary gears ) only allow a limited number of shift steps:
- a maximum of one gear can be skipped with the four-speed transmission,
- with five steps two courses
- and at six and seven stages two to four.
- with dual clutch transmissions, only an uneven number of gears can be shifted, i.e. i.e., only an even number of gears can be skipped. Often it is therefore not possible to shift directly into the most powerful gear.
The number of steps that can be shifted up and down with one shift is also referred to as the " degree of freedom " of an automatic transmission. The restriction to a certain degree of freedom is based on the fact that during a shift process no more than two clutches (usually implemented in the form of multi-plate clutches or brakes on a planetary gear set) may be actuated at the same time in order to interrupt or interrupt the flow of power between the transmission input and output sides not to block.
Not all theoretically possible jump shifts are also used, for example a shift jump from level 4 to level 2 in the four-speed automatic machine makes sense for strong acceleration (e.g. for overtaking), but the shift from 2 to 4 is not used.
In earlier automatic transmissions, the conditions for snap shifting were mapped in a complex hydraulic control system , mostly implemented as a complicated investment casting part behind a side transmission cover . For many years now, the control processes have been controlled more and more electronically .